Hi,
I don't get your point. Are you saying that you have HR system in one SAP instance and FI/FM - in another? In this case, what kind of activation do you foresee? You have to set up a system of interfaces between the two instances, so that FI/FM would receive the necessary data. Obviously, you cannot control in system 'A' what happening in system 'B' without having interaction between them.
Regards,
Eli